This invention relates to selected block copolyimide compositions each of which can be processed as a melt and is semicrystalline. In preferred embodiments, these block copolyimides exhibit recoverable crystallinity upon cooling from their respective melts.
Polyimides constitute a class of valuable polymers being characterized by thermal stability, inert character, usual insolubility in even strong solvents, and high glass transition temperature (Tg) among others. Prior art discloses that their precursors have heretofore been polyamic acids, which may take the final imidized form either by thermal or chemical treatment.
Polyimides have always found a large number of applications requiring the aforementioned characteristics in numerous industries, and currently their applications continue to increase dramatically in electronic devices, especially as dielectrics.
Different aspects regarding polyimides and copolyimides may be found in a number of publications, such as for example:
Sroog, C. E., J. Polymer Sci.: Part C, No. 16 1191 (1967).
Sroog, C. E., J. Polymer Sci.: Macromolecular Reviews, Vol. 11, 161 (1976).
Polyimides, edited by D. Wilson, H. D. Stenzenberger, and P. M. Hergenrother, Blackie, USA: Chapman and Hall, New York, 1990.
Several terms are defined below which are used in accordance with the present invention of high performance block polyimides that possess simultaneously the following desirable properties: high thermal stability, such that they can be processed in the melt, and which in preferred embodiments exhibit recoverable semicrystallinity upon crystallization from the melt.
The term xe2x80x9cmelt-processible polyimidexe2x80x9d means that the polyimide has sufficiently high thermoxidative stability and sufficiently low melt viscosity at temperatures at or above the melting point of the polyimide such that the polyimide can be processed in the melt to form a shaped object (e.g., extruded into a pellet, etc.) without the polyimide undergoing any significant degradation.
The term xe2x80x9cDSCxe2x80x9d is an acronym for differential scanning calorimetry, a thermal analysis technique widely used for accurately determining various thermal characteristics of samples, including melting point, crystallization point, and glass transition temperature. The acronym xe2x80x9cDSCxe2x80x9d is employed in text that follows below. The following definitions of slow, intermediate, and fast crystallization kinetics and related terms are based upon behavior of a given sample during DSC analysis under slow cooling, quench cooling, reheat, etc. scans during the DSC analysis (see infra for details).
The term xe2x80x9cslow crystallization kineticsxe2x80x9d means that the crystallization kinetics are such that, for a given copolyimide sample, the sample, when subjected to DSC analysis, essentially does not show any crystallization during slow cooling (i.e., cooling at 10xc2x0 C./minute) from its melt but does exhibit a crystallization peak on subsequent reheat. Furthermore, no crystallization occurs upon quench cooling.
The term xe2x80x9cintermediate crystallization kineticsxe2x80x9d means that the crystallization kinetics are such that, for a given copolyimide sample, when subjected to DSC analysis, the sample exhibits some crystallization on slow cooling and furthermore does exhibit some crystallization on reheat after slow cooling. Furthermore, there is no strong evidence for crystallization occurring upon quench cooling.
The term xe2x80x9cfast crystallization kineticsxe2x80x9d means that the crystallization kinetics are such that, for a given copolyimide sample, when subjected to DSC analysis the sample does exhibit crystallization peaks in both slow and quench cooling and furthermore no observable crystallization peak is seen on subsequent reheat of a given sample following slow cooling. After quench cooling, there may be some crystallization exhibited on reheat.
The term xe2x80x9cmelt of a polymerxe2x80x9d means the polymer exists as the melt in a liquid or substantially liquid state. If the polymer is crystalline or semicrystalline, a melt of the polymer is necessarily at a temperature greater than or equal to its melting point (Tm).
The term xe2x80x9crecoverable semicrystallinityxe2x80x9d and/or xe2x80x9crecoverable crystallinityxe2x80x9d refers to behavior occurring in a semicrystalline or crystalline polymer and specifically means the behavior that occurs when the polymer, upon heating to a temperature above its melting point and subsequent slow cooling to a temperature well below its melting point, exhibits a melting point in a reheat DSC scan. (If a melting point is not observed during the reheat DSC scan, the polymer does not exhibit recoverable crystallinity. The longer a sample is below Tm but above Tg, the greater probability it has to crystallize.)
The term xe2x80x9csemicrystalline polymerxe2x80x9d means a polymer that exhibits at least some crystalline characteristics and is partially but not completely crystalline. Most or all known polymers having crystalline characteristics are semicrystalline, but not totally crystalline, since they also have at least some amorphous characteristics. (Hence the term crystalline polymer is technically a misnomer in most or all instances where it is used, but nevertheless this term is often used.)
The term xe2x80x9cuncapped copolyimide (random or block)xe2x80x9d means a copolyimide that is the reaction product of a set of monomers (e.g., dianhydride(s) and diamine(s)) that does not include an endcapping agent.
Some significant advantages of melt processing in accordance with the present invention include processing without a solvent such that tedious and costly solvent recycling is unnecessary and can be eliminated. High thermal stability is not only essential for processing in the melt at temperatures of greater than or equal to 350xc2x0 C. but also is required for polyimides used in high temperature applications. Semicrystalline polyimides are often highly desirable in comparison to otherwise comparable polyimides that are amorphous, since the former in relation to the latter often exhibit superior properties, such as having better mechanical properties (e.g., especially higher modulus), capability for use at higher temperatures without property degradation (e.g., better solder resistance, modulus retention), higher solvent resistance, higher creep viscosities (e.g., lower tendencies for distortion of a film or other structure with time), and lower coefficients of thermal expansion.
In order for a semicrystalline polyimide to be considered melt-processible, the polyimide must possess a melting point at or below a temperature in the range of about 385xc2x0 C.-395xc2x0 C., which temperature range is a practical limit for melt processing due to both equipment capabilities/limitations and to avoid any significant thermal degradation of the polyimide. Furthermore, the polyimide also must possess a sufficiently low melt viscosity (i.e., less than or equal to a maximum of about 108 poise (which is equal to 107 Pascal-seconds), but preferably 104 poise (which is equal to 103 Pascal-seconds) or less, depending on polymer melt temperature and shear rates of the melt processing equipment). Copolymerization can be used to lower the melting temperature of a polymer (e.g., polyimide) but usually results in loss of crystallinity. Prior art polyimide compositions have been unable to achieve suitable reduction in the melting points (Tms) of the copolymeric compositions while simultaneously maintaining high degrees of semi-crystallinity in the copolymeric compositions. In the compositions of this invention, both suitable melting temperatures and high degrees of semi-crystallinity are achieved by judicious choice of comonomers and endcapping agents, and their relative amounts in each block of these block copolyimide compositions.
Polyimides that exhibit a melting point in an initial DSC heat scan and which are thereby attributed to have crystalline characteristics are disclosed in Kunimune, U.S. Pat. No. 4,923,968 to Chisso Corporation. While the copolyimides disclosed in this patent may be crystalline or semicrystalline until heated to temperatures above their melting points, the present inventors have not observed the copolyimides disclosed in this patent to exhibit recoverable recrystallinity. Indeed these copolyimides are probably substantially amorphous when cooled from their melts. Furthermore, most or all of the copolyimides disclosed in this patent are not melt-processible, because they have melting points and/or molecular weights (melt viscosities) that are too high for melt-processibility. In addition, endcapping in order to moderate the polymerization and improve melt processibility is not taught.
The selected block copolyimides of this invention overcome the drawbacks of the prior art compositions in that these copolyimides possess simultaneously these key essential propertiesxe2x80x94high thermal stability, melt-processibility, and, in preferred embodiments, recoverable crystallinity. The copolyimides of this invention can therefore be processed in the melt to form articles, which may have a predetermined shape, such as extrudates, fibers, films, and molded products comprised of these semicrystalline copolyimides.
It is known that some properties of a polymer may be best controlled and diversified by using segmented or block copolymers (the words xe2x80x9cblockxe2x80x9d and xe2x80x9csegmentxe2x80x9d regarding copolymers are used in this discussion as synonyms), wherein each of the segments or blocks provides a special and desirable character or property. A classic example is that of the styrene/butadiene block copolymers, wherein the styrene blocks provide stiffness and the butadiene blocks provide elasticity, stiffness and elasticity being two major components of toughness. The desired mechanical properties realized by block polymerization of the styrene and butadiene blocks cannot be realized by random polymerization, despite the fact that the empirical formula, molecular weight, and other parameters may be kept constant in both cases.
Thus, a large number of attempts have been made to duplicate this block concept in the case of polyimides, in order to control their properties to better fit the requirements of a given specific application. However, all these prior attempts have been either partially or totally unsuccessful. Some properties of polyimides that likely contribute to these earlier unsuccessful attempts are described infra.
First, polyimides are valuable because they are normally insoluble in most or all of the common solvents. Therefore, they also possess high solvent resistance. However, this beneficial property itself becomes a heavy burden regarding the way to apply a highly insoluble polyimide in the form of a coating, for example. Thus, the most common technique in the prior art of applying polyimides as coatings is to use a solution of the respective poly(amic acid), which is considerably more soluble, and then after the application, convert the polyamic acid to the corresponding imide by either heat or chemical means. An alternate way, also useful in the preparation of segmented polyimides, is to employ soluble oligomers or precursors (often esters), which have functional terminal groups, such as for example isocyanates, epoxides, acetylenically and ethylenically unsaturated groups, and the like, and then extend them or crosslink them. These functional groups, however, are sources of decreased thermooxidative stability, and they may cause in general deterioration of polymer properties.
Second, a special characteristic of poly(amic acids), which are for all practical purposes the reaction products of carboxylic acid dianhydrides with diamines, is that they are perpetually in a status of dynamic equilibrium, in a way that their components (diamines and dianhydrides) continuously interchange positions, depending on the factors which drive said equilibrium, in contrast with polyimides, which typically do not undergo such changes. Poly(amic acid) equilibration is further detailed by C. C. Walker, J. Polym. Sci.; Part A: Polym. Chem. Ed., 26, 1649 (1988). Reequilibration of binary poly(amic acid) mixtures is discussed by M. Ree, D. Y. Yoon, W. Volksen; xe2x80x9cMiscibility Behavior and Reequilibration of Binary Poly(Amic Acid) Mixturesxe2x80x9d, Polymeric Materials; Science and Engineering Proceedings of ACS Division of Polymeric Materials; V60; p.179-182; Spring 1989. On the other hand, equilibration in the case of aromatic polyimides requires stringent conditions, such as for example described by Takekoshi, T., xe2x80x9cSynthesis of Polyetherimides by Transimidization Reactionxe2x80x9d, preprints of symposium on Recent Advances in Polyimides and Other High Performance Polymers, Div. Of Polymer Chemistry, Am. Chem. Soc., San Diego, Calif., January 1990.
As a result of the above-described dynamic equilibrium present in a poly(amic acid), it is generally not feasible to react two different polyamic acids together with comcomitant or subsequent imidization to synthesize a segmented copolyimide having two well-defined types of segments.
In U.S. Pat. No. 5,202,412, there are disclosed polyimide copolymer oligomeric precursors that are soluble in polar solvents, a method for making the polyimide precursors, and a method for making a block polyimide copolymer, having a first imidized segment (block) and a second imidized segment (block), wherein the first imidized segment is comprised of a given polyimide precursor. The block polyimide copolymers produced by the method disclosed in this patent possess properties such that amine and anhydride rearrangment is substantially prevented 1) within the first imidized segment, and 2) between the first imidized segment and the second amic acid segment (which is precursor to the second imidized segment). There are no teachings though in this patent with regard to how block copolyimides can be melt-processible and/or exhibit recoverable recrystallinity.
In view of the discussion presented above, there are significant long-felt needs not met by the current state of polyimide art for high performance polyimides that possess high thermal stability, which can be processed in the melt (melt-processible), and which, in preferred embodiments, exhibit recoverable semicrystallinity as defined herein. This invention provides a solution to these long-felt needs.
In one embodiment of the invention is a segmented, melt-processible, semicrystalline polyimide copolymer comprising a first imidized segment and a second imidized segment prepared by the steps of:
a) preparing a first amic acid segment, the first amic acid segment being a precursor of the first imidized segment and being the reaction product of reacting a first acid dianhydride with a first diamine in a molecular ratio to obtain the first amic acid segment having two identical terminal portions selected from the group consisting of acid anhydride and amine,
whereby combinations of the first acid dianhydride and the first diamine for forming the first amic acid segment respectively are selected from the group consisting of 4,4xe2x80x2-oxydiphthalic anhydride (ODPA) and 1,3-bis(3-amino-phenoxy)benzene (APB-133) in combination; (3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; pyromellitic dianhydride (PMDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; (2,2xe2x80x2-bis-(3,4-dicarboxyphenyl)hexa-fluoropropane dianhydride (6FDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfone tetracarboxylic dianhydride (DSDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; and (2,2xe2x80x2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 1,3-bis(4-aminophenoxy) benzene (APB-134) in combination;
b) imidizing the first amic acid segment to form the first imidized segment;
c) reacting the first imidized segment with reactant(s) selected from the group consisting of 1) a second acid dianhydride and a second diamine and 2) a second amic acid segment and a linking monomer selected from the group consisting of the second acid dianhydride and the second diamine;
whereby the first imidized segment reacts with reactant(s) to form a segmented polyimide/polyamic acid copolymer comprising the first imidized segment and the second amic acid segment, with the proviso that the choice in selection of the linking monomer between diamine and dianhydride in 2) is made by choosing that linking monomer needed to result in the polyimide/polyamic acid copolymer having overall stoichiometry of about 100%,
whereby the second amic acid segment is attached to the first imidized segment through an amide group having a carbon-nitrogen bond,
whereby combinations of the second acid dianhydride and the second diamine for forming the second amic acid segment respectively are selected from the group consisting of 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(4-aminophenoxy) benzene (APB-134) in combination; and (3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic dianhydride (BTDA) and 1,3-bis(4-aminophenoxy)benzene (APB-134) in combination; and
d) imidizing the second amic acid segment to form the second imidized segment and thus resulting in formation of the segmented, melt-processible, semicrystalline polyimide copolymer.
In this invention, it is essential and required that at least one of the first imidized segment and the second imidized segment comprise imide repetition units that impart semi-crystallinity to a corresponding homopolyimide containing the imide repetition units. Furthermore, it is essential that the first imidized segment be soluble in the reaction solvent(s) at reaction temperature(s) for forming the segmented polyimide/polyamic acid copolymer.
In a preferred embodiment, a copolyimide of this invention has a stoichiometry in the range from 93% to 98%, exhibits a melting point in the range of 330xc2x0 C. to 395xc2x0 C., and exhibits recoverable crystallinity as determined by DSC analysis. Preferably, each copolyimide of this invention has a melting point under 385xc2x0 C. and, more preferably, under 380xc2x0 C.
As used herein the term xe2x80x9cstoichiometryxe2x80x9d , expressed as a percent, means total moles of dianhydride(s) in relation to total moles of diamine(s) that are incorporated in a given polyimide. If the total moles of dianhydride(s) equals the total moles of diamine(s), the stoichiometry is 100 percent. If these two numbers are not equal, either total diamine(s) or total dianhydride(s) is present in higher amount, and the stoichiometery in this case is expressed as the mole percentage of component(s) (diamine(s) or dianhydride(s)) present in lesser amount relative to that component(s) present in higher amount and expressed as 100 percent. As one example, if a polyimide sample is derived from incorporation of 0.98 mole of dianhydride(s) and 1.00 mole of diamine(s), the diamine(s) is present in higher amount and the stoichiometery is 98%.
If the stoichiometry is less than 93%, the copolyimides possess poor mechanical properties. If the stoichiometry is greater than 98%, the copolyimides are too high melting for melt-processibility to be feasible and/or do not exhibit recoverable crystallinity.
As used herein the term xe2x80x9cendcappingxe2x80x9d refers to the monofunctional component(s) (agent(s)) including, but not limited to, phthalic anhydride, naphthalic anhydride, and aniline, which cap the copolyimides to moderate the polymerization and to enhance thermoplasticity of the final melt polymerized product. Endcapping is generally done to 100% such that total moles of anhydride functionality are equal to total moles of amine functionality. Phthalic anhydride and naphthalic anhydride are suitable endcapping components in those cases where diamines are present in greater molar amounts than are dianhydrides. Aniline is a suitable endcapping component in those cases where dianhydrides are present in greater molar amounts than are diamines. The percentage of endcapping component required to afford 100% endcapping is equal to twice the value of (1xe2x88x92stoichiometry) multipled by 100. As an example, for a 100% endcapped copolyimide with 95% stoichiometry (diamine in excess), the total moles of the endcapping agent must be 10 mole percent of the total moles of the diamines, i.e., 10 moles of the endcapping agent to 100 moles of the diamines.
In another embodiment, the invention is a segmented polyimide/polyamic acid copolymer comprising a first imidized segment and a second amic acid segment prepared by the steps of:
a) preparing a first amic acid segment, the first amic acid segment being a precursor of the first imidized segment and being the reaction product of reacting a first acid dianhydride with a first diamine in a molecular ratio to obtain the first amic acid segment having two identical terminal portions selected from the group consisting of acid anhydride and amine,
whereby combinations of the first acid dianhydride and the first diamine for forming the first amic acid segment respectively are selected from the group consisting of 4,4xe2x80x2-oxydiphthalic anhydride (ODPA) and 1,3-bis(3-amino-phenoxy)benzene (APB-133) in combination; (3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; pyromellitic dianhydride (PMDA) and 1,3-bis(3-aminophenoxy)-benzene (APB-133) in combination; (2,2xe2x80x2-bis-(3,4-dicarboxyphenyl)hexa-fluoropropane dianhydride (6FDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfone tetracarboxylic dianhydride (DSDA) and 1,3-bis(3-aminophenoxy)benzene (APB-133) in combination; and (2,2xe2x80x2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 1,3-bis(4-aminophenoxy) benzene (APB-134) in combination;
b) imidizing the first amic acid segment to form the first imidized segment; and
c) reacting the first imidized segment with reactant(s) selected from the group consisting of 1) a second acid dianhydride and a second diamine and 2) a second amic acid segment and a linking monomer selected from the group consisting of the second acid dianhydride and the second diamine;
whereby the first imidized segment reacts with reactant(s) to form the segmented polyimide/polyamic acid copolymer comprising the first imidized segment and the second amic acid segment, with the proviso that the choice in selection of the linking monomer between diamine and dianhydride in 2) is made by choosing that linking monomer needed to result in the polyimide/polyamic acid copolymer having overall stoichiometry of about 100%,
whereby the second amic acid segment is attached to the first imidized segment through an amide group having a carbon-nitrogen bond,
whereby combinations of the second acid dianhydride and the second diamine for forming the second amic acid segment respectively are selected from the group consisting of 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(4-aminophenoxy) benzene (APB-134) in combination; and (3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic dianhydride (BTDA) and 1,3-bis(4-aminophenoxy)benzene (APB-134) in combination. This segmented polyimide/polyamic acid copolymer is a precursor to the aforementioned segmented polyimide copolymer.
Novel segmented (block) copolyimides having suitable molecular architectures are defined herein such that these copolyimides are semicrystalline, crystallizable from the melt, and are melt-processible. Furthermore, in preferred embodiments, these copolyimides exhibit recoverable semicrystallinity. These block copolyimides have melting points in the range from about 330xc2x0 C. to about 385xc2x0 C.-395xc2x0 C. Key melt-processibility parameters, including melting point and melt viscosity at melting temperature(s), can be tailored by appropriate choices of monomers, block length, molecular weights, and percentage of endcapping. Use of suitable molecular architecture in the inventive copolyimides also affords control of a window of temperature difference between the melting point and the glass transition temperature.
A key aspect of the invention is the surprising discovery that retention of crystallizability upon cooling from a melt of a given copolyimide while reducing melting point and other desirable properties occurs in inventive segmented (block) copolyimides when they are produced using sequenced polymerization. It is highly desirable to have semicrystalline polyimides that retain strength above the glass transition temperature and which then melt at even a higher temperature for fabrication. It has been discovered that comonomer or copolymer units that are amorphous and which destroy crystallizability when randomly placed in the chain of a crystallizable thermoplastic polyimide, unexpectedly will retain crystallizability and will lower crystalline melting when copolymerized in a sequenced way. This sequenced copolymerization is accomplished by ordered addition of monomers, or polymerization of amorphous and crystallizable polymers separately, followed by combination and chain extension. New compositions of matter have been made in this invention which are crystallizable above the glass transition temperature, and which melt at lower, more practical temperatures for fabrication of films, fibers and molded parts.
Fabrication of semicrystalline thermoplastic polyimides generally requires molding and extrusion temperatures in the vicinity of about 330-395xc2x0 C., with approximately 385-395xc2x0 C. being at the upper limit for melt processibility to be feasible using current state of the art high temperature equipment and to prevent any significant thermal degradation of polyimide from occurring. Random copolymerization may destroy crystalline characteristics, but sequenced copolymerization more readily retains crystallizability and lowers the crystalline melting point. Lower and more practical fabrication temperatures are thereby achieved with this invention.
Semicrystalline all-aromatic homopolyimides often have melting points at or above the upper limit where melt-processibility is feasible. An example is BPDA/APB-134 homopolyimide, which has a melting-point of about 400xc2x0 C. (See Comparative Example 3) and which is considered too high for practical melt-processibility.
In this invention, a key feature is that surprisingly and unexpectedly copolymerization in a sequenced manner to produce the inventive segmented copolyimides results in controlled lowering of the melting points of these copolyimides while preserving the crystallizability of these copolymides from their respective melts and which thereby imparts recoverable crystallinity characteristics to these block copolyimides.
The segmented (block) copolyimides of this invention are characterized in having structures comprised of A//B segments or blocks, where A represents an amorphous or semicrystalline segment and B represents a semicrystalline segment. The A segment (block) is termed a soft segment, while the B segment (block) is termed a hard segment. While both A and B can be semicrystalline provided the A segment is sufficiently soluble in a suitable solvent (e.g., DMAC, NMP) at process temperature(s) for forming the A/B polyimide/poly(amic acid) copolymer, A and B segments are always structurally different and are not identical. Preferably, the A segment is amorphous or only slightly to moderately semicrystalline while the B segment is semicrystalline. Key attributes of the A segment include solubility of homopolyimide comprised of A segments in organic solvents (DMAC, etc.) and ability to reduce the melting point of block copolymers comprised of B segments without destroying the recoverable crystallinity. Key attributes of the B segment include its possessing recoverable crystallinity and its affording a melting point to the block copolyimide of equal to or less than about 395xc2x0 C., and preferably less than or equal to 385xc2x0 C.
The invention is in one embodiment a segmented polyimide/polyamic acid copolymer comprising a first imidized segment and a second amic acid segment.
The first imidized segment, which is derived from a first amic acid segment as precursor, is obtained by first reacting a first acid dianhydride with a first diamine in a molecular ratio to obtain the first amic acid segment having two identical terminal portions selected from the group consisting of acid anhydride and amine. Subsequently, the first amic acid segment is imidized to form the first imidized segment. Preferably, the first imidized segment is anhydride terminated.
The first acid dianhydride and the first diamine for forming the first imidized segment via the first amic acid segment as precursor (independently of the second acid dianhydride and the second diamine) are respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; 6FDA and APB-133 in combination; DSDA and APB-133 in combination; and 6FDA and APB-134 in combination. The first acid dianhydide and the first diamine are preferably respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; and 6FDA and APB-134 in combination; more preferably respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; and PMDA and APB-133 in combination; and most preferably respectively selected from the group consisting of ODPA and APB-133 in combination, and BPDA and APB-133 in combination. For special applications requiring a material having low dielectric constant, the first acid dianhydride and the first diamine are preferably either 6FDA and APB-134 in combination, or 6FDA and APB-133 in combination, respectively.
The second amic acid segment in the segmented polyimide/polyamic acid copolymer is obtained by reacting the first imidized segment with reactant(s) which are either 1) a second acid dianhydride and a second diamine or 2) a second amic acid segment and a linking monomer selected from the group consisting of the a dianhydride and a diamine; to form the second amic acid segment, which is attached to the first imidized segment through an amide group having a carbon-nitrogen bond.
In case of 1) above, suitable combinations of the second acid dianhydride and the second diamine for forming the second amic acid segment (independently of the first acid dianhydride and the first diamine) are respectively selected from the group consisting of BPDA and APB-134 in combination; and BTDA and APB-134 in combination. The second acid dianhydide and the second diamine are, respectively, preferably BPDA and APB-134 in combination.
In case of 2) above, suitable second amic acid segments are BPDA/APB-134 and BTDA/APB-134. Examples 22-27 exemplify this case 2) with the second amic acid segment being BPDA/APB-134, which contained 98% of the stoichiometric amount of BPDA and hence had excess amino functionality. Hence, in these examples having excess amino functionality, a dianhydride, rather than a diamine, is used as a linking monomer to link the first imidized segment with the second amic acid segment and to raise the overall stoichiometry of the segmented copolyimide towards about 100%. In Examples 22-27, BPDA was used as linking monomer, but any other dianhydride can be used as linking monomer in this invention. Similarly, in cases where the second amic acid has excess dianhydride functionality, any diamine can be used as the linking monomer according to the invention.
When the second acid dianhydride and the second diamine are most preferably BPDA and APB-134, respectively, suitable combinations of the first acid dianhydride and the first diamine for forming the first imidized segment via the first amic acid segment as precursor are selected respectively from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; 6FDA and APB-133 in combination; DSDA and APB-133 in combination; and 6FDA and APB-134 in combination. Preferably, the first acid dianhydride and the first diamine for forming the first amic acid and first imidized segments are respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; and PMDA and APB-133 in combination. More preferably, the first acid dianhydride and the first diamine for forming the first amic acid and first imidized segments are respectively selected from the group consisting of ODPA and APB-133 in combination, and BPDA and APB-133 in combination. Most preferably, the first acid dianhydride and the first diamine for forming the first amic acid and first imidized segment are respectively ODPA and APB-133 in combination.
The invention is in another embodiment a segmented melt-processible polyimide copolymer comprising a first imidized segment and a second imidized segment.
The first imidized segment is obtained by reacting a first acid dianhydride with a first diamine in a molecular ratio to obtain a first amic acid segment as precursor having two identical terminal portions selected from the group consisting of acid anhydride and amine. Subsequently, the first amic acid segment is imidized to form the first imidized segment.
The first acid dianhydride and the first diamine for forming the first imidized segment via the first amic acid segment as precursor (independently of the second acid dianhydride and the second diamine) are respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; 6FDA and APB-133 in combination; DSDA and APB-133 in combination; and 6FDA and APB-134 in combination. The first acid dianhydride and the first diamine are preferably respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; and 6FDA and APB-134 in combination; more preferably respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; and PMDA and APB-133 in combination; and most preferably respectively selected from the group consisting of ODPA and APB-133 in combination, and BPDA and APB-133 in combination. For special applications requiring a material having low dielectric constant, the first acid dianhydride and the first diamine respectively are preferably either 6FDA and APB-134 in combination, or 6FDA and APB-133 in combination.
The second imidized segment of the segmented copolyimide of this invention is obtained by reacting the first imidized segment with reactant(s) which are either 1) a second acid dianhydride and a second diamine or 2) a second amic acid segment and a linking monomer selected from the group consisting of the a dianhydride and a diamine; to form the second amic acid segment, which is attached to the first imidized segment through an amide group having a carbon-nitrogen bond and subsequently imidizing the second amic acid segment to form the second imidized segment, whereby combinations of the second acid dianhydride and the second diamine for forming the second segment (independently of the first acid dianhydride and the first diamine) are respectively selected from the group consisting of BPDA and APB-134 in combination; and BTDA and APB-134 in combination. The second acid dianhydide and the second diamine are, respectively, preferably BPDA and APB-134 in combination.
When the second acid dianhydride and the second diamine are most preferably BPDA and APB-134, suitable combinations of the first acid dianhydride and the first diamine for forming the first segment are respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; PMDA and APB-133 in combination; 6FDA and APB-133 in combination; DSDA and APB-133 in combination; and 6FDA and APB-134 in combination. Preferably, the first acid dianhydride and the first diamine for forming the first segment are respectively selected from the group consisting of ODPA and APB-133 in combination; BPDA and APB-133 in combination; and PMDA and APB-133 in combination. More preferably, the first acid dianhydride and the first diamine for forming the first segment are respectively selected from the group consisting of ODPA and APB-133 in combination, and BPDA and APB-133 in combination. Most preferably, the first acid dianhydride and the first diamine for forming the first segment respectively are ODPA and APB-133 in combination.
The segmented, melt-processible polyimide copolymers of this invention has a second segment (B segment) that is semicrystalline. Preferably, the second segment is present in the copolymer at a level of greater than or equal to 60 weight percent. More preferably, the semicrystalline segment is present in the copolymer at a level in the range of 65 to 85 weight percent, and still more preferably, the semicrystalline segment is present in the copolymer at a level in the range of 75 to 85 weight percent.
The segmented, melt-processible polyimide copolymers of this invention are comprised of a first imidized segment that has number average molecular weight (as determined by gel permeation chromatography on the precursor segmented polyimide/polyamic acid copolymers) in the range of about 2,000 to about 20,000; preferably the first segment has Mn in the range of 3,000 to 15,000, more preferably the first segment has Mn in the range of 4,000 to 10,000, and most preferably the first segment has Mn in the range of 4,000 to 8,000.
The number average molecular weight (Mn) of the first imidized segment can be set quite closely by using stoichiometric imbalance calculations (i.e., employing the Carothers equation) to determine the required off-stoichiometry amounts of the first dianhydride and the first diamine necessary for a given molecular weight of first imidized segment. Such calculations were made as are described in many polymer textbooks, such as, for example, Principles of Polymerization, Third Edition, by George Odian, John Wiley and Sons, Inc., New York (1991), p. 82-87.
As illustrated in some of the examples, number average molecular weights for selected first imidized segments as determined by titrimetic analysis were in excellent agreement with the calculated molecular weights based on stoichiometric imbalance.
This invention encompasses both segmented, melt-processible, semicrystalline polyimide copolymers and their precursors, segmented polyimide/polyamic acid copolymers. Conversion of amic acid segments to corresponding imidized segments can be effected using thermal imidization and/or chemical imidization as is known to those skilled in this art (see following paragraph).
As illustrated in many textbooks and other references (e.g., for example, see Polyimides, edited by D. Wilson, H. D. Stenzenberger, and P. M. Hergenrother, Blackie, USA: Chapman and Hall, New York, 1990), reaction of a dianhydride(s) with a diamine(s) in solution initially affords a poly(amic acid). Typical reaction temperatures are ambient temperature to about 100xc2x0 C. The poly(amic acid) that results can subsequently be converted to the corresponding polyimide (and water) by either heating the poly(amic acid) to elevated temperature(s) (e.g., about 200-400xc2x0 C.) and/or subjecting the poly(amic acid) to chemical imidization using reagents such as triethylamine in combination with acetic anhydride.
Diamines
APB-133xe2x80x941,3-bis(3-aminophenoxy)benzene
APB-134xe2x80x941,3-bis(4-aminophenoxy)benzene (=RODA)
RODAxe2x80x941,3-bis(4-aminophenoxy)benzene (=APB 134)
Dianhydrides
BPDAxe2x80x943,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride
BTDAxe2x80x943,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic dianhydride
DSDAxe2x80x943,3xe2x80x2,4,4xe2x80x2-diphenylsulfone tetracarboxylic dianhydride
6FDAxe2x80x942,2xe2x80x2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride
ODPAxe2x80x944,4xe2x80x2-oxydiphthalic anhydride
PMDAxe2x80x94pyromellitic dianhydride
General
AAxe2x80x94Acetic anhydride
CTExe2x80x94Coefficient of thermal expansion DSCxe2x80x94Differential scanning calorimetry
hr(s)xe2x80x94hour(s)
lb(s)xe2x80x94pound(s)
RPMxe2x80x94Revolutions per minute
TEAxe2x80x94Triethylamine
gxe2x80x94gram
GPaxe2x80x94Gigapascals
GPCxe2x80x94Gel permeation chromatography
J/gxe2x80x94Joules per gram
Mnxe2x80x94Number average molecular weight (determined by GPC unless otherwise specified)
Mn(tit)xe2x80x94Number average molecular weight determined titrimetrically
Mwxe2x80x94Weight average molecular weight (determined by GPC unless otherwise specified)
Mw(tit)xe2x80x94Weight average molecular weight determined titrimetrically
MPaxe2x80x94Megapascals
O/P(X)//Q/R(Y) Block copolyimide comprised of first imidized segments derived from O and P monomers, where O is the first dianhydride and P is the first diamine, and second imidized segments derived from Q and R monomers, where Q is the second dianhydride and R is the second diamine. The first and second imidized segments, respectively, are present at levels of X mole percent and Y mole percent in the block copolyimide.
PAxe2x80x94Phthalic anhydride
Tgxe2x80x94Glass transition temperature
Tmxe2x80x94Melting point (xc2x0 C. unless otherwise specified)
Solvents
DMACxe2x80x94N,N-dimethylacetamide
NMPxe2x80x94N-methyl-2-pyrrolidinone
Miscellaneous
Poly(amic acid)=polyamic acid=initial reaction product of a dianhydride with a diamine and precursor to a polyimide.